They are not worth having ie more trouble than worth - I originally got them just to determine how much gas was left, but nowdays I pretty much know how much is left by time off grid.
I use a small notice white board that I write time and date on every time I change over bottles. I have two bottles mounted on drawbar and only use one bottle at a time.
Replacements are cheap as chips at the big green shed, so not worth rehabilitating IMO.
__________________
Possum; AKA:- Ali El-Aziz Mohamed Gundawiathan
Sent from my imperial66 typewriter using carrier pigeon, message sticks and smoke signals.
Those gauges are pressure gauges and measure the pressure in the cylinder.
The pressure in the cylinder will remain relatively constant (at constant ambient temperature) while there is still some liquefied gas in the cylinder.
The gauge reading will only start to decrease when there is no liquid remaining in the cylinder at which point you are almost empty and just using the residual gas.